An injection molding machine for injecting a melted substance such as a synthetic resin by means of hydraulic pressure so as to produce molded products normally comprises components for carrying out a gate cut and a product injection which are carried out in different steps.
A conventional type of the injection molding machine carries out a gate cut and a product ejection by using the same ejector pin driven by a hydraulic ejector cylinder. In this case, the gate cut is performed by a full stroke of a hydraulic ejector and, after resin in a cavity is cooled down, the hydraulic ejector is again operated for ejecting a product.
Another type of the conventional injection molding machine is provided with a gate cut pin and an ejector pin. Immediately after the resin is injected or while pressure is applied, the gate cut pin is operated by the hydraulic ejector cylinder for carrying out a gate cut. After the gate cut is complete, the gate cut pin is returned to its initial position. Subsequently, after the resin in the cavity is cooled down, a product is ejected out by operating the gate cut pin and the ejector pin driven by the hydraulic ejector cylinder.
Either of the above-described types of the injection molding machine has a problem that the gate cut and the product ejection are carried out by operation of the hydraulic ejector at the same speed (flow) and pressure. That is, the gate cut may be carried at a speed and a pressure which have been appropriately set for the product ejection. In this case, the speed and the pressure are insufficient for carrying out the gate cut, resulting in that a gate trace will remain on the gate cut surface and a molding cycle is unnecessarily prolonged.
On the contrary, in the case when the hydraulic ejector operation is set at the speed and the pressure which are appropriate for the gate cut, the speed is too high for the product ejection and cracks may be generated in the product.
There is another problem that a typical hydraulic injection molding machine which has been recently developed is provided with a single electromagnetic flow control valve and a single electromagnetic pressure control valve for controlling speed (flow) and pressure of actuators, respectively, and incapable of simultaneously controlling the speed and the pressure of a plurality of actuators. Consequently, it is necessary to carry out resin injection, gate cut, and product ejection one after another, waiting for a certain time duration between each of the steps. This significantly prolongs the entire cycle of injection molding.
Moreover, when a gate cut as carried out, the resin of the gate cut portion should be pushed into either to the product side or to the sprue runner portion. If a resin pressure remains in the cavity, the gate portion can be cut off by increasing the pressure of the hydraulic ejector for operating the gate cut pin. However, if the injection molding machine is used for a long time in such a condition, the gate cut pin is tilted by the pressure resistance. This may cause defective products and rupture of the metallic molds. The sprue runner may not be easily removed from the metallic molds.
In the case when an electric mechanism is used as ejector driving means, it is similarly difficult to select a preferable speed for each of the gate cut and the product ejection.
In view of the above-described problems, a primary object of the present invention is to provide a gate-cut and ejection control apparatus and method for an injection molding machine which is capable of operating at a preferable speed and pressure for each of the gate cut and the product ejection.
Another object of the present invention is to provide a gate-cut and product ejection control apparatus and method for an injection molding machine which suppresses generation of defective products and rupture of metallic molds which may be caused by the resin pressure in the metallic molds.